Width for Benevolence - CSS?

My blog is currently using the Benevolence theme which I like, but I just wish the column were wider; it would be ideal if it fit to the screen. The only thing I've been able to find that could potentially change this is CSS, but I know absolutely nothing about it. Does anyone know if a) CSS is a possible solution and b) an easy way to do this?
Any help would be greatly appreciated. Thank you!

b) There are only a few here in the forums with any CSS experience, and they are only here randomly, so you really should have some knowledge of CSS and how it relates to the markup (HTML) or it can be quite frustrating.

The one thing to remember is that there are still a fair amount of people out there using 1024 x 768 resolution, which means the overall width of your theme should not exceed 1000px (and I prefer to stick with 990px max just for a little breathing space). Horizontal scrolling is the #3 thing out of 10 that people on the web don't like to do.

Delete everything in the CSS edit window (appearance > edit CSS) and paste the following into the CSS edit window and then click "preview".

There are other things that will have to be done, but this will give you an idea of what it will look like at 990px overall width. Basically it is an increase of 290px to the content area since I left the sidebar the same width and location.

It looks like you had the CSS upgrade already and everything looks fine.

Now what you will have to do is to create a new header image, upload it to the media library and then put the URL of that image into the proper location in the CSS which I have shown below. Add the following to the #masthead